1. Field of the Invention
The present invention relates to a driving method and a driving device for a display device such as a liquid crystal display device which displays an image by sequentially driving pixels arranged in a matrix form.
2. Description of the Prior Art
A method as described below has heretofore been employed, for example, to display an image on an active matrix driving liquid crystal display or the like by using interlaced scanning television video signals obtained by scanning the original image every other line.
When the interlaced scanning television video signals use, for example, 240 horizontal scanning lines per field, pixels are arranged in 240 lines, the number of lines corresponding to that of horizontal scanning lines, on the liquid crystal display panel of the liquid crystal display device, in which a video signal representing one horizontal scanning line is sampled by a clock signal of the timing that matches the number of pixels per line and the arrangement of the pixels so that data voltages obtained by sampling are applied to the corresponding pixels in a particular line. This operation is sequentially performed on all lines of pixels to complete the display of an image for one field.
In this case, the video signal representing, for example, the first horizontal scanning line of an odd-numbered field and the video signal representing the first horizontal line of an even-numbered field both use the pixels in the same first line to display on the liquid crystal display panel, not interlaced with each other for display.
FIG. 1 is a diagram illustrating the interlaced scanning video signals conceptually arranged in the form of an original image to explain the above driving method in a specific manner. In FIG. 1, the original image is horizontally scanned eight times, the first, third, fifth, and seventh horizontal scans producing video signals for the odd-numbered field and the second, fourth, sixth, and eighth scans producing video signals for the even-numbered field.
FIG. 2 is a conceptual diagram illustrating an image reproduced from the interlaced scanning video signals and displayed on an interlaced scanning display device. The image on the display device comprises ten pixels per line, the number of lines being set to eight to match the number of scans of the original image. Also, the pixels are arranged in such a manner as to be shifted horizontally by one-half of a pixel between the odd-numbered and even-numbered lines.
In using the interlaced scanning video signals with the display device shown in FIG. 2, the sampling of a video signal representing one horizontal scanning line in an odd-numbered field is performed at the timing of sampling A indicated by " " in FIG. 1 in accordance with the arrangement of the pixels in the odd-numbered lines, while the sampling of a video signal representing one horizontal scanning line in an even-numbered field is performed at the timing of sampling B indicated by "o" in FIG. 1 in accordance with the arrangement of the pixels in the even-numbered lines. That is, in the displayed image of FIG. 2, the pixels in the first line, for example, are used, in the odd-numbered field, to display the first horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling A, while the pixels in the second line are used, in the even-numbered field, to display the second horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling B.
FIG. 3 is a conceptual diagram illustrating an image reproduced from the interlaced scanning video signals and displayed on a liquid crystal display panel. FIG. 3(1) shows the displayed image of an odd-numbered field, FIG. 3(2) shows the displayed image of an even-numbered field, and FIG. 3(3) shows an image produced by superposing the odd-numbered field image on the even-numbered field image.
The displayed image shown in FIG. 3 comprises ten pixels per line, the number of lines being set to four to match the number of horizontal scanning lines for one field of the interlaced scanning video signals. That is, the liquid crystal display panel shown comprises four lines of ten pixels.
In using the interlaced scanning video signals with the liquid crystal display panel shown in FIG. 3, the display of an odd-numbered field is performed as shown in FIG. 3(1): the pixels in the first line are used to display the first horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling A, the pixels in the second line used to display the third horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling B, the pixels in the third line used to display the fifth horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling A, and the pixels in the fourth line used to display the seventh horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling B. On the other hand, the display of an even-numbered field is performed as shown in FIG. 3(2): the pixels in the first line are used to display the second horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling A, the pixels in the second line used to display the fourth horizontal scanning line of the original image represented by the video signal sampled at the timing of sampling B, the pixels in the third line used to display the sixth horizontal line of the original image represented by the video signal sampled at the timing of sampling A, and the pixels in the fourth line used to display the eighth horizontal line of the original image represented by the video signal sampled at the timing of sampling B. Thus, two types of sampling timing different from line to line are selected alternately according to the shifted arrangement of the pixels between the odd-numbered and even-numbered lines on the liquid crystal display panel.
Thus, the image of the odd-numbered field shown in FIG. 3(1) and the image of the even-numbered field shown in FIG. 3(2) are displayed alternately on the liquid crystal display panel, producing a visual result as shown in FIG. 3(3) in which the image of the odd-numbered field is superposed on the image of the even-numbered field.
As described above, in the prior art driving method for displaying an image on a non-interlaced scanning display device using interlaced scanning video signals, the pixels in the same line are used to alternately display the image reproduced from the video signal of an odd-number field and the image reproduced from the video signal of an even-numbered field. As a result, the prior art has the problem that the display quality drops substantially compared with the display screen provided by an interlaced scanning display device. This tendency becomes even more appreciable as the size of the display screen becomes larger. In particular, in the case of displaying an image having diagonal lines as shown in FIGS. 1 to 3, a marked drop in the reproducibility of the diagonal lines is noted as is apparent from the comparison between FIG. 2 and FIG. 3(3).